<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>样式演示</title>
    <style>
        div{
            border: 1px solid red;

            width: 60%;

            height: 500px;

            margin: auto;

        }
    </style>
</head>
<body>
<div>
    第一个div
</div>
</body>
</html>